1. Field of the Invention
The present invention relates to a wrapping machine and, more particularly, to a vegetable and fruit wrapping machine for wrapping a soft or flexible tray. The present invention also pertains to a method of folding a tray in a piece of wrapping film clamped and stretched over a wrapping area defined in such a wrapping machine, thereby wrapping an object to be wrapped.
2. Description of the Prior Art
In a conventional wrapping machine, for example, one disclosed in the specification of Japanese Patent Laid-Open No. 90010/1983, a piece of wrapping film is stretched over a wrapping area defined in the machine, and both lateral edges of the film are respectively clamped by front and rear pressing members. When, in this state, a tray on a delivery means is pushed up to a wrapping position, the film is tensely stretched while covering the tray from the upper side thereof. Then, the edge portions of the film are gathered together tightly underneath the tray by a folding means, thereby wrapping the tray with the film. More specifically, the folding means in the above wrapping machine, for example, is arranged such that a movable rear folding member is longitudinally moved relative to a fixed front folding member so as to come toward and away from the latter, and right and left folding members are opened and closed with respect to each other below the rear folding member in response to the longitudinal movement of the rear folding member. Further, a multiplicity of mounts for mounting objects to be wrapped are provided on the delivery means so as to project therefrom upwardly, the mounts being able to tilt inwardly when abutting against the rear folding member and the right and left folding members.
When the rear folding member is advanced and the right and left folding members are closed or moved toward each other, these folding members push a piece of wrapping film toward the underside of a tray placed on the mounts and abut against these mounts so as to tilt the same. Simultaneously with this tilting operation, the delivery means is moved downwardly. In consequence, the tray is gradually transferred to the rear folding member from the rear end of its lower surface, and while doing so, the rear and both lateral edge portions of the film are gathered together tightly underneath the tray.
Thereafter, the tray is transported forwardly by the rotation of a conveyor belt and is thereby transferred from the rear folding member to the front folding member. In the course of this transfer, the film abuts against the front folding member underneath the tray, and the film is also folded from the front side thereof, whereby the portions of the film folded from the right and left sides are overlaid on the portion of the film folded from the rear side, and the portion of the film folded from the front side is further laid thereon, thus forming a fold portion underneath the tray. Then, the rear folding member is retracted, and the right and left folding members are opened or separated from each other in response to the retraction of the rear folding member.
In the above-described wrapping film folding operation, when the rear folding member enters the space underneath the tray in such a manner as to contact the undersurface of the tray, it is easy for the rear folding member to collide with the rear edge of the undersurface of the tray at the beginning of this entry. In the case of wrapping a soft or flexible tray particularly, the above collision may cause the tray to be deformed so as to crush soft contents thereof, which leads to a deterioration in the value of commodities.
For this reason, it is conventional practice to allow the rear folding member to abut against the mounts at a position spaced slightly downwards from the undersurface of the tray on the mounts so as to prevent the aforementioned collision. In consequence, the right and left folding members which are positioned below the rear folding member are further separated from the undersurface of the tray. Accordingly, when the tray is wrapped while being gradullay transferred to the rear folding member from the rear end of its undersurface, the mounts are tilted by the right and left folding members to a substantial degree at both lateral sides of the undersurface of the tray, resulting in a relatively large space occurring between the tilted mounts and the undersurface of the tray, so that the tray is supported only by the rear folding member and the front mounts which are not tilted. Accordingly, during a folding operation, the tray easily oscillates laterally and may slide into the rear folding member and slant in a very unstable state.
In view of the above, the right and left folding members may be positioned above the rear folding member, and the tray may be placed on the right and left folding members when being folded in a piece of wrapping film. However, it is necessary when doing so to move the right and left folding members so as to enter the film area prior to the rear folding member. It is therefore very difficult to appropriately set the timing relationship between the rear folding member and the right and left folding members from the viewpoint of the folding procedure according to which these folding members effect their respective folding operations underneath the tray. Accordingly, it is desired that the conventional structures of the rear folding member and the right and left folding members should be improved.